Electrochemical Synthesis of Individual Core@Shell\nand Hollow Ag/Ag₂S Nanoparticles

Abstract

This\nletter presents an electrochemical methodology for structure-tunable\nsynthesis, characterization, and kinetic monitoring of metal–semiconductor\nphase transformations at individual Ag nanoparticles. In the presence\nof HS^– in aqueous solution, the stochastic collision\nand adsorption of Ag nanoparticles at a Au microelectrode initiates\nthe partial anodic transformation of Ag to Ag₂S at each\nparticle. A single continuous current transient is observed for each\nAg nanoparticle reacted. The characteristic shapes of the transients\nare distinct from previously reported amperometric recordings of electrochemical\nreactions involving single nanoparticles and are highly uniform at\na constant applied potential. The average maximum current increases\nwhile the event duration decreases as a function of increasing potential.\nIndependent of applied potential, the electrochemical transformation\nevent abruptly stops after converting ∼80% of the Ag in the\nnanoparticle to Ag₂S, a self-terminating process that does\nnot occur for bulk Ag electrodes under similar conditions. The resulting\nproducts are a mixture of core@shell Ag@Ag₂S nanoparticles\nwith and without voids in the core, as characterized by transmission\nelectron microscopy (TEM) and energy-dispersive X-ray spectroscopy\n(EDX). Both the frequency and size of voids increase at more positive\npotentials. The average size of the core@shell nanoparticles determined\nby coulometric analysis of the current transients agrees well with\nTEM measurements.